Subwatershed 7.07 includes the Cowleech Fork of the Sabine River and covers 177 square miles in the upper Sabine Basin. The waterbody is not designated as a segment in the Texas Surface Water Quality Standards (TSWQS) and the general standards for surface water are applicable. Cowleech Fork is one of seven subwatersheds in the Lake Tawakoni watershed and represents 23% of the 756 square-mile total drainage area of the reservoir. Lake Tawakoni is listed as Segment 0507 in the TSWQS. Cowleech Fork is intermittent from its origin at the Sabine Basin Divide, north of Celeste, downstream to the confluence of Long Branch, receiving stream for the City of Greenville wastewater treatment plant in south Greenville. Due to effluent from the city, Cowleech Fork is perennial downstream of Long Branch. During high stream flow, Greenville may divert water from Cowleech Fork into city lakes near the northern city limits.

The 1996 Sabine River Authority Assessment of Water Quality identified the Cowleech Fork Subwatershed as an area of concern due to poor water quality. Water quality concerns and possible concerns in this subwatershed include dissolved oxygen, chlorides, sulfates, total dissolved solids, nutrients, fecal coliform and ambient toxicity. Preliminary results indicate the cause of toxicity to be organic chemicals (possibly pesticides).

Due to the extensive use of Lake Tawakoni for recreation and as a water supply reservoir, a special study was initiated in the spring of 1998 in the Cowleech Fork Subwatershed to identify the sources of water quality impairments. Since 1998 was an unusually dry year, the study was extended into 1999. The lethal and sublethal results seen in the ambient toxicity tests were the primary concern of the study. Sampling was conducted to substantiate non-compliance with Texas Surface Water Quality Standards for oxygen, chlorides, sulfates, and total dissolved solids. Additional water quality parameters typically collected by SRA included fecal coliform bacteria, nutrients, total organic carbon, pH, conductivity, temperature, rainfall, and weather conditions.

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